Photographic films



3,043,695 PHGTQGRAPHIC FILMS Francis Peter Alles, Westfield, N.J., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Feb. 27, 1959,'Ser. No. 795,923 8 Claims. (Cl. 9683) This invention relates to photography and more particularly to photographic stripping film elements. The invention still more particularly relates to dimensionallystable dry-stripping elements for use in the photogravure art in the preparation of intaglio printing members.

The most common method of forming resists for intaglio printing members is by the so-called carbon tissue process. This process consists in exposing imagewise, a pigmented gelatin layer which has been sensitized by potassium bichromate. Such a layer is usually coated on a paper base. hardened imagewise. The exposed element is then wetted with water and adhered to the printing element such as a a copper plate. Application of hot Water to the back of the Upon exposure, the gelatin layer becomes adhered element softens the gelatin and allows the paper base to be stripped off. The soft or unexposed gelatin is then washed away with warm Water leaving a pigmented gelatin relief image on the printing element which can then be etched imagewise to provide the well-known gravure printing surface. This process has disadvantages and requires very skillful manipulation to produce satisfactory printing plates. -For example, the exposure must be carefully controlled. Over-exposure causes the gelatin to harden to too great a depth and, hence, stripping of the paper base becomes diflicult, if not impossible. Underexposure does not provide suificient buildup of the relief image. It is also necessary to sensitize the gelatin layer with potassium bichromate just prior to use so that the user must carry out the sensitizing operation, rather than the manufacturer of the carbon tissue. Long exposure times are required by the process. They are necessitated by the fact that such systems are sensitive primarily in the short wavelength (i.e., 350 to 550 m portion of the spectrum. This is a tremendous disadvantage since there is no known practical way of increasing the spectral response of such a system. Dimensional stability is also a great disadvantage with such elements.

It has been proposed to overcome the disadvantages of the bichromated gelatin by using a gelatino-silver halide emulsion coated on a hydrophobic film permanent support with a gelatin or other soluble stripping layer between the emulsion and the support. The use of non-soluble, tacky stripping layers has been proposed but they have proved deficient in one way or another. In the interests of dimensional stability and for other reasons it has been proposed to coat a so-called temporary support (e.g., a cellulose derivative) with a stripping layer, a permanent" support, e.g., a cellulose derivative membrane and a silver halide emulsion with the necessary intervening anchoring layers.

While the use of gelatino-silver halide emulsions offers tremendous advantages over the gelatin-potassium bichromate light-sensitive layer and the stripping elements offer a considerable advantage in time-saving, they also have other disadvantages than those mentioned above. For example, when the element is exposed and developed by the usual photographic methods andis adhered to the printing member, considerable skill is required to remove the temporary support and also the cellulosic membrane or Patented July 10, %62

2 copolymer containing 9699.5% by weight of the former with (2) 60 to parts by weight of a vinylidene chloride addition copolymer containing at least 35% vinylidene chloride, preferably a vinylidene chloride/unsaturated permanent support; so that the subsequent hot water etch ester/itaconic acid copolymer, e.g., a vinylidene chloride/methyl acrylate/itaconic acid copolymer containing said ingredients in the respective percentages, by weight, of 35-96%, 3.5 to 40% and 0.5 to 25%,an anchor layer of gelatin which may contain up to 20%, based on the weight of the gelatin, of a water-soluble polyvinyl pyrrolidone which under some conditions improves anchorage and coating uniformity. A layer of soluble gelatin may be coated between the anchor layer and the emulsion layer. The opposite side of the support is coated with a vinylidene chloride/methyl acryl ate/itaconic acid copolymer and a gelatin subbing layer as described in Alles et al. US. Patent 2,627,088.

The above stripping layers, composed of a mixture of n-butyl methacrylate/itaconic acid and vinylidene chloride/methyl acrylate/itaconic acid copolymers, may be dried at l20-200 and preferably from -190 F.

(The pH of the mixture of 'copolymeric dispersion is usually from about 2.3 to 2.5; however this is not critical and the pH may be adjusted to higher levels with a suitable alkali, e.g., ammonium hydroxide, without harmful effect. 8

While the support film may be composed of any hydrophobic organic polymer, including cellulose monocarboxylic acid esters, e.g., cellulose acetate, cellulose acetate butyrate, cellulose propionate and cellulose nitrate; super polyamides, e.g., polyhexamethylene adipamide and polyhexamethylene sebacamide; polyesters, e.g., polyethylene terephthalate, polyethylene terephthalate/isophthalate and poly(transparahexahydroxylene)-terephalate, it is preferably composed of an oriented polymethylene terephthalate corresponding to the polyesterification product of a polymethylene glycol of 2-10 carbon atoms with terephthalic acid of the type described in Whinfield and Dickson U.S. Patent 2,465,319.

The coating weight, based on the dry weight of the dr stripping layer composed of the mixture of polymers (1) and (2), may vary from 10 to 25 mg./dm. The lower coating weights within this range generally give higher stripping tension.

The film supports when made of orientable polymers and particularly polymethylene terephthalates can be made by casting the polymer, applying the vinylidene chloride copolymer layer to one surface of the cast film. The coated film can then be oriented, heat-set and a water permeable colloid layer applied, all after the manners disclosed in US. patent Alles et a1. 2,627,088, and Alles et al. 2,728,941. After the above treatments, the mixture of n-butyl methacrylate/itaconic acid and vinylidene chloride/ methyl acrylate/itaconic acid is coated on the opposite side of the base and dried. A gelatin sublayer is applied and the film given a further heat treatment to relieve stresses in the film as described in Alles 2,779,684. 7 g The light-sensitive gel-atino-silver halide emulsion should be freefrom hardening agents as should a gelatin la-yer if one isplaced contiguous therewith. However, the emulsion layer after exposure to an object field or image must be capable of being differentially hardened in either a hardening developer or a hardening bleach bath so that a relief image can be formed by washing away the unexposed and unhardened emulsion. In addition, the ratio of gelatin to silver halide should be high, i.e., a relatively large quantity of gelatin to a relatively small quantity of silver halide. A satisfactory range is from 2 to 5 parts of gelatin to 1 part of silver halide. Any desirable light-sensitive silver halide may be used,

' i.e., silver chloride, silver bromide, silver iodobromide,

etc.

The copolymers may be made by any convenient method well-known in the art. methacrylate/itaconic acid copolymer may be made as follows.

A S-necked 1 liter flask was equipped with a stirrer, nitrogen inlet tube,'thermo meter, and a reflux condenser and placed in a hot water bath, Intothe fiask were placed 350 ml. of distilled water, 12.0 grams of sodium lauryl sulfate, 294.0 gnams of inhibitor-free n-butyl methacrylate, and 6.0 grams of itaconic acid. The air in the flask was displaced with nitrogen, and a solution of 1.18 gramsof potassium persulfate and 0.60 gram of sodium metabisulfite in 26.0 ml. of water was added. The mixture was stirred under nitrogen and the temperature was raised to 50 C. After a short induction period, the reaction started (as indicated by a temperature rise). The polymerization was conducted for 3.3 hours, the temperature being held between 50 C. and 70 C. The reaction mixture was cooled and placed in a suitable container for use. The milky white dispersion analyzed for 44.0% poly(n-butyl methacrylate co itaconic acid, 98/2).

The vinylidene chloride/methyl acrylate/itaconic acid copolymer was made as described in Swindells U.S. 2,698,235 granted December 28, 1954. This copolymer can be admixed with water and the two-component copolymer previously described.

In making resists from a photographic film element of the invention, it can be exposed by one of the usual methods to produce the desired latent image in the photo sensitive layer. For instance, in making a gravure plate, the film can be exposed through a half-tone screen for a suitable time and then through a continuous tone positive or vice versa. Other conventional types of screens and sequences of exposure can be used, including the screens and procedures disclosed in Kott US. Patent 2,628,903 of Feb. 17, 1953. The exposed film can then be developed in a hardening developer as described in Boyer et al. US. 2,650,878 of Sept. 1, 1953, and in White et'al. US. Patent 2,638,417 of May 12, 1953, and further treated For example, the n-butyl aosasos and used to form an etched plate as disclosed in said patents.

The invention will now be illustrated but is not intended to be limited by the following examples wherein the photographic film is made in the substantial absence of actinic light and all parts and percentages are by weight, unless otherwise indicated.

Example I A polyethylene tereph thalate film made by the procedures set forth in U.S. Patent 2,627,088 was coated with a 4% aqueous solution of the copolymer of Example 11 of U.S. Patent 2,698,235 noted above to form an anchoring layer. The film was then molecularly oriented by stretching in the manner described in US. Patent 2,627,088 to form a film base of about 4 mils in thickness.

A gelatin subbing solution having the formula:

was coated over the copolymeric anchor layer. An antihalat-ion layer comprising gelatin chrome alurmand Acid Magenta O (Rowes Colour Index No. 692) is subse- V quently applied over this anchor layer after the following treatments are applied to the opposite side of the base.

The aqueous dispersion of poly n-butylmethacrylate/ itaconic acid (98/2) described in the preceding preparation Was diluted to obtain a 15% solids dispersion. An aqueous dispersion of a vinylidene chloride/methyl acrylate/itaconic acid was made according to Example I of Patent 2,698,235 in proportions of monomer by weight of 15 2. The aqueous dispersion was diluted to 15% solids. Portions of the above aqueous dispersions were mixed in a ratio of 80% of the n-butyl methacrylate/ itaconic acid copolymer to 20% of the vinylidene ch1oride/methyl acrylate/itaconic acid copolymer. To the resulting mixture there was added 4% of the total weight of the solution of a 5% alcohol-water Saponin solution. The pH of the resulting mixture was 2.5. It was then coated on the opposite surface. of the polyethylene terephthalate film in an amount to give a dry coating weight of 10 ting/dm. at a speed of 40 feet per minute.

The coating was dried at- 190 F. A gelatin anchor layer having the following composition was applied over the above copolymer layer.

The film was then heat-relaxed at C. in the manner taught in Patent 2,779,684. Over the gelatin anchor layer there was coated a'gelatin solution of the following composition:

Percent by weight Gelatin 5.500 Potassium chloride .032 Saponin .045 Glycerine .158 Ethyl alcohol 1.820 Thymol .010 Water to make 100.00

This gelatin composition was applied to give a soluble gelatin layer having a coating weight of about 50 to 60 mg./dm. based on the weight of the gelatin.

Over the resulting soluble gelatin layer there was coated an orthochromatically sensitized gelatino-silver chlorobromide emulsion containing 25 mole percent of silver chloride. The coating weight of the resulting emulsion layer was about 60 to 65 mg. of silver halide per sq. dm. which gave a layer thickness of about 0.6 mil.

The resulting dried film structure was exposed in a vacuum printing frame through a -line conventional gravure screen for 8 seconds to a 25-watt tungsten lamp placed 8 feet from such screen. The film was then exposed through a step wedge for 9 seconds to a 15-watt lamp at 8 feet. The exposed film was then processed in the following manner:'

(1) Developed in a two-bath hardening developer solution as follows: i

A solution (3 minutes):

Sodium metabisulfite grams 5 Pyrogallol do 5 Anionic wetting agent (Eumercin NB) 10% aqueous ml 2 Water to make 1 liter. B solution (2 minutes):

Sodium carbonate (monohydrate) grams 100 Anionic wetting agent (Eumercin NB 10% aqueous) ml 2 Water to make 1 liter.

(2) Washed for 1 minute in water at 68 F.

, minutes for satisfactory removal.

' (4) Washed for 10 minutes in water at 68 F.

(5 The film was then dried.

The processed film was then adhered, emulsion side down, to a gravure copper plate, by standard procedure as practiced in the art for laying down gravure resist material. The base was then dry-stripped from the film. The layer of the mixture of copolymers (a) and (b) adhering to the gelatin was removed by dissolving the layer This required from 1 to 4 The copper plate containing the film was then immersed in a bath of hot water at 125 F. for ten minutes to dissolve away all unexwith methyl ethyl ketone.

posed, unhardened gelatin; thus forming a relief of varying thickness (in direct proportion to silver densities) of hardened gelatin on the copper.

After thorough drying of the gelatin relief image and covering over the base "f"; areas of copper with asphaltum as is common practice in the art, the stepwedge relief images were etched into the copper in normal gravure fashion with ferric chloride solutions to form a satisfactory printing plate.

Example 11 Example I was repeated except that the stripping layer was coated from a 15% aqueous solution of a mixture composed of 70% of n-butyl methacrylate/itaconic acid copolymer and 30% by weight of vinylidene chloride/ methyl acrylate/itaconic acid copolymer. All other conditions and operations of manufacture, exposure, processing and lay-down .on a copper plate were identical with Example I. Stripping of the base from the layer composed of the mixture of copolymers after lay-down was satisfactory and somewhat easier than in Example I due to a decrease in stripping tension. The normal gravure procures after stripping'were carried out as described in Example I to give a satisfactorily etched, good quality printing plate.

. Example III Example I was again repeated using in place of the stripping layer of that example a stripping layer coated from a 15% aqueous solution of a mixture composed of 60% of n-butyl methacrylate/itaconic acid copolymer and 40% of vinylidene chloride/methyl acrylate/itaconic acid copolymer. All other conditions and operations of manufacture, exposure, processing and lay-down on the gravure plate were identical with Example I. Stripping of the base from the film after lay-down was satisfactory and stripping tension was slightly less than in Example II. The normal gravure procedures after stripping were carried out as described in Example I to give a satisfactorily etched, good quality printing plate.

Example IV Example V Example I was repeated except that the stripping layer was coated from a aqueous solution of a mixture of 50% by weight of n-butyl methacrylate/itaconic acid copolymer and 50% by weight of vinylidene chloride/ methyl acrylate/itaconic acid copolymer. The gelatin anchor layers were coated from a solution having the following composition, all percentages being by weight.

The pH adjusted to 6 by addition of aqueous sodium hydroxide. 60 feet per minute to give a dry coating weight of 14 mg./dm. The rest. of the conditions of drying, exposing and testing were the same as in Example I. Stripping of the base from the film after lay-down was satisfactory and stripping tension was slightly less than in Example I.

Any of the vinylidene chloride copolymers containing at least 35% vinylidene chloride in U.S. Patents 2,627,088 and 2,698,235 can be substituted in equivalent amount for the specific one described above. The unsaturated ester can be ethyl, methyl, propyl or butyl methacrylate or aorylate, vinyl chloride, acrylonitrile or methacrylonitrile. In the copolymers 35 to 96% vinylidene chloride, 3.5 to 40% unsaturated ester and 0.5 to 25% itaconic acid should be present.

The copolymers in the stripping layer may vary in the ratios of monomeric components. For example, in the case of the n-butyl methacrylate/itaconic acid copolymer the percent by weight of n-butyl methacry-late may range from 96 to 99.5, itaconic acid, of course, making up the The preferred range of n butyl percentage difference. methacrylate, however, is 98 to 99%. In the case of the vinylidene chloride/methyl acrylate/itaconic acid copolymer the practical and preferred ranges are as follows:

Benzene, toluene, xylene, dioxane, acetone, turpentine and mixtures of two or more of said solvents, and other organic solvents may be used to remove the copolymeric stripping film after lay-down.

While the silver halide emulsion and the gelatin sublayer are usually colorless, dyes may be incorporated in either or both of these layers for various reasons. For example, the clear gelatin layer, if one is used, may contain an antihalation dye and thus make it unnecessary to have an antihalation layer on the back of the base. I If desired, various photographic sensitizing dyes, e.g., cyanine, pseudocyanine, carbocyanine, merocyanine and styryl dyes, can be added to the silver halide emulsions to extend their sensitivity to the green and red regions of the visible spectrum.

An advantage of the novel dry-stripping films of the invention is that they are dependable and give satisfactory results. They are simpler and more economical to manufacture than those generally used in the photogravure art, taking cognizance, of course, of the superiority of film elements using silver halide emulsions over the gelatinbichrom-ate elements on paper supports used in the very early processes.

Another and outstanding advantage of the invention is the ease of control of the stripping tension during manufacture. This is of paramount importance for an acceptable product in the graphic arts trade.

While the novel stripping layers may be used as disclosed above in conjunction with 'variousbases, they are The anchoring solutions were coated at P7 particularly efiicacious when used on the orientable polyester films predominating in polymethyleneterephthalate as described above. This offers the important advantage 7 of dimensional stability which is not possible with the stripping films of the prior art.

What is claimed "is: i 1. 'A photographic stripping film comprising a flexible hydrophobic organic polymer film bearing onone sur-' face, in order, a thinlayer of a mixture of (1.) 40 to 80 parts by weight of an n-butyl methacrylate/itaconic acid monomeric units of the copolymer are present in the I respective amounts by weight of 35% to 96%, 3.5% to 40% and 0.5% to 25%, an anchor layer of a Water-permeable organic colloid comprising gelatin and a gelatinosilver halide emulsion layer.

2. A film as defined in claim 1 wherein said copolymer is a vinylidene chloride/methyl acrylate/itaconic acid copolymer.

3. A film asdefined in claim 1 wherein there is a layer of water-soluble gelatin between said anchor layer and said emulsion layer.

vinyl-2-py1rolidone) in anamount from 10-20% based,

on the weight of gelatin.

5. A stripping film as defined in claim 1 wherein said polymer film is 3 to 8 mils in thickness.

6. A stripping film as defined in claim 1 wherein said polymer film is biaxially oriented and essentially coniprises a polymethylene terephthalate containing 2 to 10 methylene groups.

7.. A stripping film as defined in claim 1 wherein said polymer film has on the opposite surface, in order, a layer of said vinylidene chloride/unsaturated ester/itaconic acid copolymer and an antihalation layer.

8. A stripping film as defined in claim 1 wherein said polymer film is biaxially oriented polyethylene terephthalate.

References'Cited in the file of this patent UNITED STATES PATENTS 2,698,235 Swindells Dec. 28, 1954 2,698,242 Saner Dec. 28, 1954 FOREIGN PATENTS 591,231 Great Britain Aug. 12, 1947 

1. A PHOTOGRAPHIC STRIPPING FILM COMPRISING A FLEXIBLE HYDROPHOBIC ORGANIC POLYMER FILM BEARING ON ONE SURFACE IN ORDER A THIN LAYER OF A MIXTURE OF (1) 40 TO 80 PARTS BY WEIGHT OF AN N-BUTYL METHACRYLATE/ITACONIC ACID COPOLYMER CONTAINING 96% TO 99.5% BY WEIGHT OF THE FORMER AND 0.5% TO 4% BY WEIGHT OF THE LATTER MONOMERIC UNITS AND (2) 60 TO 20 PARTS BY WEIGHT OF A VINYLIDENE CHLORIDE/UNSATURATED ESTER/ITACONIC ACID COPOLYMER WHEREIN SAID ESTER IS TAKEN FROM THE GROUP CONSISTING OF METHYL, ETHYL PROPYL AND BUTYL ACRYLATE AND METHACRYLATE, ACRYLONITRILE, METHACRYLONITRILE AND VINYL CHLORIDE AND THE MONOMERIC UNITS OF THE COPOLYMER ARE PRESENT IN THE RESPECTIVE AMOUNTS BY WEIGHT OF 35%TO 96%, 3.5% TO 40% AND 0.5% TO 25%, AN ANCHOR LAYER OF A WATER-PERMEABLE ORGANIC COLLOID COMPRISING GELATIN AND A GELATINOSILVER HALIDE EMULSION LAYER. 